A ball screw device has a configuration in which a plurality of balls roll along a ball load rolling path, which is constituted by a spiral ball rolling groove formed in a screw shaft, and a ball load rolling groove, which is formed in a nut member, which are opposite to each other. The ball screw device has a ball circulation path configured to circulate the balls that terminate the rolling along the ball load rolling groove to the ball load rolling groove again, and according to a relative rotation between the screw shaft and the nut member, the balls endlessly circulate from the ball circulation path to the ball load rolling path.
In the following Patent Literature 1, a pipe type ball circulation part is disclosed as a ball circulation part that forms the ball circulation path. The ball circulation part is formed by combining a first split body and a second split body. A mating surface between the first split body and the second split body is formed along the ball circulation path, and the ball circulation part has a configuration that can be split into upper and lower portions in a height direction. The ball circulation part is positioned with respect to a nut member (a ball load rolling path) by inserting the second split body under a pipe into an attachment hole of the nut member and fixing the first split body over the pipe to the nut member so as to be covered from above.